1. Technical Field
The present invention relates to an image carrier cleaning device which removes residual non-transferred toner after a transfer operation of a toner image, an image carrier cleaning method, and an image forming apparatus including an electrophotographic device such as an electrostatic copy machine, a printer, or a facsimile provided with the image carrier cleaning device.
2. Related Art
Among image forming apparatuses, there is known an image forming apparatus disclosed in JP-A-H04-275569, where the image forming apparatus adopts a charging method in which a surface of a photoconductor is largely charged to a negative polarity by a charging brush after a transfer operation of a toner image and the photoconductor is adjusted to a predetermined negatively charged potential by means of a corona charging operation with a positive polarity using a corona charger in a rotation direction of the photoconductor from the charging brush. According to the charging method of the photoconductor, the amount of produced ozone can be reduced and the photoconductor can be uniformly charged.
However, a residual non-transferred toner and an external additive separated from the toner remain on the photoconductor after the transfer operation of the toner image. In the image forming apparatus disclosed in JP-A-H04-275569, when the residual non-transferred toner and the external additive are removed by a cleaning brush before arriving at the charging brush, the charging brush and the corona charger are prevented from being polluted, and hence a satisfactory charging operation can be continuously carried out.
However, when the residual non-transferred toner and the external additive after the transfer operation of the toner image are removed by the cleaning brush before the charging operation performed by the charging brush, an elevated portion may be formed between the photoconductor and an intermediate transfer belt. In addition, the intermediate transfer belt may be bent or the image may be omitted halfway due to the elevated portion. Particularly, in recent image forming apparatuses, toner having a small particle diameter of 5 μm or less and a high degree of circularity of 0.96 or more has been used for the purpose of obtaining a high definition. However, when such toner is used, the bending phenomenon or the image halfway omission may easily occur.
The reason is as below. That is, when the toner having a small particle diameter of 5 μm or less and a high degree of circularity of 0.96 or more is used, the residual non-transferred toner can easily exit the cleaning blade. For this reason, in order to reliably remove the residual non-transferred toner, a contact pressure applied from the cleaning blade to the photoconductor needs to be larger than that of the known image forming apparatus. However, if the contact pressure of the cleaning blade is large, an external additive is removed as well as the residual non-transferred toner. Additionally, if the external additive is excessively removed by the cleaning blade, most of the external additive exiting the cleaning blade and moving toward a transfer device is removed. For this reason, the elevated portion is easily formed between the photoconductor and the intermediate transfer belt, and hence the bending phenomenon or the image halfway omission occurs.
In addition, when the amount of the external additive exiting the cleaning blade is small, chattering or curling of the cleaning blade occurs due to a large contact pressure.